Composition for ceramic substrate and ceramic circuit component

ABSTRACT

There is disclosed a composition for a ceramic substrate comprising a mixture of: powdered borosilicate-based glass comprising about 5% to 17.5% by weight of B 2 O 3 , about 28% to 44% by weight of SiO 2 , 0% to about 20% by weight of Al 2 O 3 , and about 36% to 50% by weight of MO (where MO is at least one selected from the group consisting of CaO, MgO, and BaO), and a powdered ceramic; in which the amount of the powdered borosilicate-based glass is about 40% to 49% by weight based on the total amount of the composition for a ceramic substrate, and the amount of the powdered ceramic is about 60% to 51% by weight based on the total amount of the composition for a ceramic substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 09/550,826,filed Apr. 18, 2000, now U.S. Pat. No. 6,376,055.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composition for a ceramic substrateand a ceramic circuit component, and more particularly to a compositionfor a ceramic substrate which can be sintered at a temperature as low as1,000° C. or less, and a ceramic circuit component, such as amultilayered integrated circuit component and a thick-film hybridcircuit component, which is fabricated using the composition for theceramic substrate.

2. Description of the Related Art

Currently, alumina substrates are predominantly used as ceramicsubstrates. In order to obtain an alumina substrate, firing must beperformed at a temperature as high as approximately 1,600° C., andthereby, for example, when a multilayered circuit component isfabricated using the alumina substrate, a metal having a high meltingpoint must be used for internal conductors. However, the metal having ahigh melting point generally has a high resistance and is thusunsuitable for conductors used for multilayered circuit components inwhich higher frequencies and higher speeds are increasingly in demand.

Accordingly, glass-ceramic substrates having a firing temperature of1,000° C. or less, which enable use of metals having a low resistance asinternal conductors, such as Au, Ag, Ag—Pd, Ag—Pt and Cu, have beenreceiving attention and various types of glass-ceramic substrates havebeen developed.

For example, Japanese Examined Patent Publication No. 3-53269 disclosesa low-temperature sinterable ceramic substrate which is obtained bymixing 50% to 64% by weight of powdered glass and 50% to 35% by weightof powdered Al₂O₃, followed by sintering at 800 to 1,000° C.

However, with respect to such a substrate in which glass is loaded atthe rate of 50% or more, the proportion of crystalline substances in thesintered substrate is decreased, and thus the dielectric loss of thesubstrate may be increased or it may be difficult to obtain highmechanical strength, which is disadvantageous. Additionally, when athick-film electrode and a thick-film resistor are baked on the surfaceof the sintered substrate, the substrate easily deforms under theinfluence of the remaining glass, which is also disadvantageous.

As a solution to the problems described above; the composition of thepowdered glass as a starting material may be arranged so as to be easilycrystallized after sintering, thus increasing the proportion ofcrystalline substances in the sintered substrate. However, with asubstrate having a large proportion of glass in the starting material,such as with a glass load of 50% or more, strain in the substrate causedby the crystallization of glass during firing is influential, anddeformation, such as warpage and cracking, easily occurs in the sinteredsubstrate, which is disadvantageous.

Japanese Examined Patent Publication No. 4-42349 discloses alow-temperature sinterable ceramic composition in which 40% to 50% byweight of powdered glass, composed of 10% to 55% by weight of MO (whereM is at least one of Ca and Mg), 0% to 30% by weight of Al₂O₃, 45% to70% by weight of SiO₂, and 0% to 30% by weight of B₂O₃, and 60% to 50%by weight of powdered Al₂O₃, are mixed and fired at 1,100° C. or less.The above patent publication also discloses that by increasing theproportion of the powdered Al₂O₃, in the starting material, a transversestrength of 2,600 to 3,200 kgf/cm² (255 to 314 MPa) can be obtained.However, such transverse strength is lower than the transverse: strength(approximately 350 MPa) of the alumina substrate which is used as acircuit substrate, and higher strength is desired.

The substrate disclosed in the same patent publication has a coefficientof thermal expansion in the range from 4.0 to 5.7 ppm/° C. It has beenbelieved that a substrate having a low coefficient of thermal expansionis preferable on the assumption that a silicon chip (IC) having acoefficient of thermal expansion of 3.5 ppm/° C. is directly mounted onthe substrate. However, due to the development of a mounting method inwhich stress is relieved using a cushioning material such as anunderfilling, a mismatch in the coefficient of thermal expansion betweenthe ceramic substrate and the silicon chip does not greatly cause aproblem. In addition, the size of the silicon chip has not increased ashas been expected.

Under the circumstances where the ceramic substrate is joined to alarger resin substrate as a motherboard, a mismatch in the coefficientof thermal expansion between the ceramic substrate and the resinsubstrate is rather influential. For example, a typical glass epoxy(FR-4) has a coefficient of thermal expansion of 14 to 16 ppm/° C., andan epoxy reinforced with Aramid fibers has a coefficient of thermalexpansion of approximately 8 ppm/° C. If a degree of mismatch in thecoefficient of thermal expansion between the ceramic substrate and theresin substrate is increased, the reliability of the connection betweenthe two substrates is lost, which is disadvantageous.

SUMMARY OF THE PRESENT INVENTION

To overcome the above described problems, preferred embodiments of thepresent invention provide a composition for a ceramic substrate and aceramic circuit component fabricated using the same, in which theproblems described above can be solved.

More specifically, in accordance with the preferred embodiments of thepresent invention, a composition for a ceramic substrate used forelectronic circuits with a firing temperature of 1,000° C. or less isprovided, thus enabling metals having a low resistance, such as Au, Ag,Ag—Pd, Ag—Pt and Cu, to be used as internal conductors. In a ceramicsubstrate obtained by firing the composition, it is possible to achievea transverse strength of 300 MPa or more, a Q factor (1 MHZ) of 1,400 ormore, and a coefficient of thermal expansion of 6.0 ppm/° C. or more.

One preferred embodiment of the present invention provides a compositionfor a ceramic substrate, comprising a mixture of: powderedborosilicate-based glass comprising about 5% to 17.5% by weight of B₂O₃,about 28% to 44% by weight of SiO₂, 0% to about 20% by weight of Al₂O₃,and about 36% to 50% by weight of MO (where MO is at least one selectedfrom the group consisting of CaO, MgO and BaO); and a powdered ceramic;in which the amount of the powdered borosilicate-based glass is about40% to 49% by weight based on the total amount of the composition for aceramic substrate, and the amount of the powdered ceramic is about 60%to 51% by weight based on the total amount of the composition for aceramic substrate.

Preferably, the composition for the ceramic substrate has a coefficientof thermal expansion of about 6.0 ppm/° C. or more after sintering.

Preferably, the powdered ceramic contains powdered alumina.

The borosilicate-based glass may contain at least one alkali metal oxideselected from the group consisting of Li₂O, K₂O and Na₂O, the amount ofthe alkali metal oxide being about 5 parts by weight or less relative to100 parts by weight of the total amount of the B₂O₃, SiO₂, Al₂O₃, andMO.

The borosilicate-based glass may contain at least one compound selectedfrom the group consisting of TiO₂, ZrO₂, Cr₂O₃, CaF₂ and CuO, the amountof the compound being about 5 parts by weight or less relative to 1 00parts by weight of the total amount of the B₂O₃, SiO₂, Al₂O₃,and MO.

Another preferred embodiment of the present invention provides a ceramiccircuit component comprising a substrate obtained by molding andsintering the composition for the ceramic substrate described above anda conductive circuit provided in association with the substrate.

In the ceramic circuit component, the conductive circuit preferablycontains at least one metal selected from the group consisting of Ag, Auand Cu as a principal ingredient.

According to the composition for the ceramic substrate of the presentinvention as described above, since low-temperature sintering at 1,000°C. or less is enabled, when a ceramic circuit component provided with aconductive circuit containing a metal having a low resistance, such asan Ag-based metal or a Cu-based metal is fabricated, firing can beperformed simultaneously with the metal for the conductive circuit. Inthe ceramic substrate fabricated using the composition, it is possibleto achieve a high mechanical strength, a low dielectric constant, a lowloss and a high coefficient of thermal expansion required for thesubstrate. Accordingly, a ceramic circuit component, such as amultilayered ceramic circuit component, having satisfactorycharacteristics and high reliability can be obtained.

In particular, since it is possible to achieve in accordance with thecomposition for the ceramic substrate of the present invention, acoefficient of thermal expansion of about 6.0 ppm/° C. or more,satisfactory matching in the coefficient of thermal expansion with amotherboard composed of, for example, an epoxy resin, is obtained,resulting in high connection reliability.

In accordance with the composition for the ceramic substrate of thepresent invention, when the borosilicate-based glass contains at leastone alkali metal oxide selected from the group consisting of Li₂O, K₂Oand Na₂O with an amount of about 5 parts by weight or less relative to100 parts by weight of the total of B₂O₃, SiO₂, Al₂O₃ and MO, thesoftening and flow properties of the glass are accelerated, and even ifthe glass amount is reduced in the composition for the ceramicsubstrate, a relatively low sintering temperature can be maintained.

In accordance with the composition for the ceramic substrate of thepresent invention, when the borosilicate-based glass contains at leastone compound selected from the group consisting of TiO₂, ZrO₂, Cr₂O₃,CaF₂ and CuO with an amount of about 5 parts by weight or less relativeto 100 parts by weight of the total of B₂O₃, SiO₂, Al₂O₃, and MO, thecrystallization of the glass is accelerated, and it is possible tofurther improve the high mechanical strength and the low loss of theresultant ceramic substrate.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a multilayered ceramic circuit component 1in accordance with an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is characterized in that, with respect to acomposition for a ceramic substrate composed of a mixture of powderedborosilicate-based glass and a powdered ceramic, such as powderedalumina, which can be fired at low temperatures, by using a powderedborosilicate-based glass having a composition which is easilycrystallized after sintering as a sintering additive, and by setting theglass amount lower than the ceramic amount, the proportion ofcrystalline substances in the sintered ceramic substrate is increased,and a low-temperature sinterable ceramic substrate having a highmechanical strength, a coefficient of thermal expansion as high as about6.0 ppm/° C. or more, and a low loss can be obtained.

As described above, the crystallization of glass during firing causesstrain in the ceramic substrate and deformation may occur in thesintered ceramic substrate. However, since the amount of glass used inthe present invention is about 49% by weight or less, which is smallerthan the amount of the ceramic, the deformation of the ceramic substrateresulting from the crystallization of the glass during firing can beadvantageously suppressed.

The glass functions as a sintering additive for sintering the ceramicsubstrate at 1,000° C. or less due to softening and viscous flow in thefiring process; In order to secure the function as the sinteringadditive, the amount of glass added must be about 40% by weight or more.

As described above, a crystal phase of wollastonite, anorthite, and thelike is easily precipitated from the glass component which is in thesoftened and viscous flow state, thus enabling the sintered ceramicsubstrate to have a high mechanical strength and a low loss.

The glass is composed of B₂O₃ and SiO₂ as glass network-forming oxides,MO as a glass network-modifying oxide (where MO is at least one oxideselected from the group consisting of CaO, MgO and BaO), and Al₂O₃ as aglass network intermediate oxide which exhibits the network-formingcapacity in collaboration with the network-modifying oxide. Theproportion of the oxides is adjusted so that the glass functions as thesintering additive for sintering the ceramic substrate at 1,000° C. orless and the crystal phase is easily precipitated in the sinteringprocess.

Of the B₂O₃ and SiO₂ glass network-forming oxides, B₂O₃ is an oxide forreducing the softening temperature and accelerating viscous flow, andthe amount thereof is selected at about 5% to 17.5% by weight. If theamount is less than about 5% by weight, the softening and flowproperties of the glass are degraded. If the amount is more than about17.5% by weight, the water resistance of the glass becomes insufficient,and the properties of the ceramic substrate may be changed when used ina high temperature and high humidity environment, and also the Q factorof the glass itself is decreased, thus decreasing the Q factor of theresultant ceramic substrate.

In the glass network-forming oxides, the SiO₂ amount is selected atabout 28% to 44% by weight. If the SiO₂ amount is less than about 28% byweight, the dielectric constant of the remaining glass itself isincreased and a ceramic substrate having a low dielectric constantcannot be obtained. On the other hand, if the amount is more than about44% by weight, the softening and flow properties of the glass aredegraded and thus the ceramic substrate cannot be sintered at 1,000° C.or less. The crystallization of the glass is also inhibited, and thuscharacteristics such as a high mechanical strength and a low loss cannotbe achieved, and the coefficient of thermal expansion of the ceramicsubstrate is decreased.

The amount of Al₂O₃, as the glass network intermediate oxide is 0% toabout 20% by weight. The Al₂O₃, acts as a glass intermediate oxide andstabilizes the glass structure. If the Al₂O₃, amount exceeds about 20%by weight, the softening and flow properties of the glass are degradedand the ceramic substrate cannot be sintered at 1,000° C. or less. Thecrystallization of the glass is also inhibited, and thus characteristicssuch as a high mechanical strength and a low loss cannot be achieved.

MO as the glass network-modifying oxide is a component for acceleratingthe softening and flow properties of the glass and the amount thereof isselected at about 36% to 50% by weight. If the MO amount is less thanabout 36% by weight, the softening and flow properties of the glass aredegraded and the coefficient of thermal expansion of the resultantceramic substrate is decreased. On the other hand, if the MO amountexceeds about 50% by weight, the glass structure becomes unstable, and aglass of stable quality cannot be obtained.

In the production of the glass having the composition described above,in order to further accelerate the softening and flow properties, atleast one alkali metal oxide selected from the group consisting of Li₂O,K₂O and Na₂O may be incorporated with an amount of about 5 parts byweight or less relative to 100 parts by weight of the total of B₂O₃,SiO₂, Al₂O₃ and MO. If the amount of the alkali metal oxide exceedsabout 5 parts by weight, the electrical insulating properties of theglass are degraded, the electrical insulating properties of the sinteredceramic substrate are degraded, and the coefficient of thermal expansionof the ceramic substrate is also decreased.

In order to further increase the high mechanical strength and the lowloss of the resultant ceramic substrate by accelerating thecrystallization of the glass in the firing process, at least onecompound selected from the group consisting of TiO₂, ZrO₂, Cr₂O₃, CaF₂and CuO may be incorporated with an amount of about 5 parts by weight orless relative to 100 parts by weight of the total of B₂O₃, SiO₂, Al₂O₃and MO. If the amount of the compound exceeds 5 parts by weight, thesintered ceramic substrate has an excessively high dielectric constantsince the dielectric constant of the glass is increased.

The composition for the ceramic substrate described above isadvantageously used for producing a ceramic circuit component providedwith a substrate obtained by forming and firing the composition and aconductive circuit formed in relation to the substrate.

FIG. 1 is a sectional view which schematically shows a multilayeredceramic circuit component 1, which is an example of the ceramic circuitcomponent described above, in accordance with an embodiment of thepresent invention. In brief, the multilayered ceramic circuit componentI includes a ceramic substrate 2 and a conductive circuit 3 which isformed in and/or on the surface of the ceramic substrate 2.

The ceramic substrate 2 is fabricated by firing a ceramic green compactobtained by laminating a plurality of green sheets containing thecomposition for the ceramic substrate described above, and includes aplurality of ceramic layers 4 obtained by firing the plurality of greensheets, respectively.

The conductive circuit 3 is formed, for example, by firing a conductivepaste containing a conductive component comprising at least one metalselected from the group consisting of Ag, Au and Cu as a principalingredient simultaneously with the ceramic green compact. The conductivecircuit 3 is provided with, for example, external conductors 5, 6 and 7which are formed on the surface of the ceramic substrate 2, and isprovided with, for example, internal conductors 8, 9, 10, 11 and 12which are formed in the ceramic substrate 2, and is also provided withvia-hole joints 13, 14, 15, 16, 17, 18 and 19.

The internal conductors 8 and 9 are opposed to each other with aspecific ceramic layer 4 therebetween to constitute a capacitor section20. The via-hole joints 16 to 19 and the internal conductors 10 to 12are alternately connected to each other to constitute an inductorsection 21.

EXAMPLES

Compositions for ceramic substrates in the present invention will now bedescribed in detail based on examples.

Table 1 shows ingredients of the compositions for ceramic substratesproduced in the examples.

TABLE 1 Glass Composition Glass Ceramic MO Al₂O₃ B₂O₃ SiO₂ Others AmountAmount Sample (% by weight) (% by (% by (% by (parts by (% by (% by No.CaO MgO BaO weight) weight) weight) weight) weight) Type weight) 1 36 00 16 6 42 — 49 Alumina 51 2 45 0 0 13 14 28 — 46 Alumina 54 3 50 0 0 79.5 33.5 — 45 Alumina 55 4 37 0 0 20 8 35 — 45 Alumina 55 5 46 0 0 5 742 — 47 Alumina 53 6 46 0 0 5 7 42 — 44 Alumina 56 7 35 0 5 12 8 40 — 44Alumina 56 8 38 0 0 17 5 40 — 48 Alumina 52 9 40 0 0 8 12 40 — 42Alumina 58 10 42 0 0 5.5 10 42.5 — 48 Alumina 52 11 42 0 0 5 9 44 — 49Alumina 51 12 42 0 0 9.5 6 42.5 — 48 Alumina 52 13 42 0 0 5.5 10 42.5 —48 Alumina 42 Forsterite 10 14 45 0 0 5 7 43 TiO₂:1.0 48 Alumina 52 1530 10  0 12 8 40 ZrO₂:1.0 44 Alumina 56 16 40 0 0 9 8 43 Cr₂O₃:1.0 46Alumina 54 17 39 6 0 5 7 43 CaF₂:1.0 46 Alumina 54 18 45 0 0 5 7 43CuO:0.5 46 Alumina 54 19 45 0 0 0 17.5 37.5 CuO:0.25 41 Alumina 59 20 400 0 0 16 44 CuO:0.25 45 Alumina 55 21 40 0 0 9 8 43 CuO:0.5 48 Alumina52 22 37 0 0 20 8 35 Li₂O:1.0 40 Alumina 60 23 37 0 0 20 8 35 K₂O:3.0 42Alumina 58 24 37 0 0 20 8 35 Na₂O:2.0 41 Alumina 59 25 34 0 0 10 12 44 —46 Alumina 54 26 52 0 0 8 8 32 — 44 Alumina 56 27 37 0 0 22 11 30 — 48Alumina 52 28 47 0 0 10 3 40 — 48 Alumina 52 29 38 0 0 11 19 32 — 44Alumina 58 30 49 0 0 18 7 26 — 46 Alumina 54 31 39 0 0 7 8 46 — 48Alumina 52 32 35 5 0 5 13 42 — 38 Alumina 62 33 40 0 0 7 13 40 — 52Alumina 48

First, oxides or carbonates, as starting materials, were prepared so asto satisfy the glass compositions shown in Table 1. A mixture was meltedin a Pt crucible for one hour at 1,300 to 1,700° C. according to theglass composition. After the melt was quenched, grinding was performedand powdered glass for each sample was obtained. Additionally, Table 1shows, with respect to MO (CaO, MgO and BaO), Al₂O₃, B₂O₃ and SiO₂,which were starting materials, the compositional ratios in units of “%by weight”, and with respect to other starting materials, such as TiO₂,the compositional ratios are shown in units of “parts by weight”relative to 100 parts by weight of the total of MO, Al₂O₃, B₂O₃ andSiO₂.

Next, each powdered glass obtained as described above and a powderedceramic, such as powdered alumina, were mixed at a ratio between the“glass amount” and the “ceramic amount” shown in Table 1, and a solvent,binder and a plasticizer were added thereto, followed by fully mixing.By employing the doctor blade process, green sheets were obtained.

Based on the green sheets for the individual samples obtained asdescribed above, several forms of specimens were prepared, andevaluations were conducted with respect to “transverse strength”,“relative dielectric constant (∈_(r))”, “Q”, “coefficient of thermalexpansion”, and “precipitated crystal phase”.

TABLE 2 Firing Transverse Sample Temperature Strength Coefficient ofThermal Precipitated No. ° C. MPa ε_(r) Q Expansion (ppm/° C.) CrystalPhase 1 900 330 8.5 1,900 7.8 A 2 860 340 8.8 2,500 8.8 A, W 3 870 3308.7 3,200 8.3 A, W 4 880 325 8.6 2,800 8.3 A, W 5 820 350 7.2 4,000 7.9A, W 6 880 335 7.6 4,300 7.6 A, W 7 880 335 8.7 2,000 7.5 A 8 890 3408.7 1,700 8.2 A 9 990 350 8.6 1,700 7.4 A 10 850 310 7.9 2,900 7.4 A, W11 860 310 7.8 3,200 7.2 A, W 12 880 320 8.2 1,900 7.9 A, W 13 860 3007.7 3,200 7.7 A, W, F 14 880 330 7.8 5,000 7.6 A, W 15 890 335 8.8 2,5006.3 A, W 16 860 320 8.5 2,600 7.5 A, W 17 870 315 8.7 2,700 6.7 A, W 18880 340 7.8 3,700 7.5 A, W 19 890 325 8.4 2,500 6.9 A, W 20 860 315 8.62,500 6.0 A, W 21 850 325 8.8 2,600 7.5 A, W 22 880 330 8.7 2,100 8.2 A23 880 330 8.7 2,100 8.2 A 24 880 330 8.7 1,900 8.2 A 25 1,000   densesintered compact unobtainable 26 880 250 8.2 1,200 8.5 A, W 27 1,000  dense sintered compact unobtainable 28 1,000   dense sintered compactunobtainable 29 820 300 8.8 1,000 7.4 A 30 880 280 9.1 1,500 8.9 A 31900 290 7.9 1,700 5.8 A,W 32 1,000   dense sintered compact unobtainable33 840 280 7.9 2,500 7.1 A

First, after a predetermined number of green sheets for each sample werelaminated and cut in predetermined sizes, firing was performed at thefiring temperature shown in Table 2, and thus a sintered compact wasobtained. By an abrasive process, the dimensions thereof were set at 36mm long, 4 mm wide and 3 mm thick. With respect to the sintered compactthus obtained for each sample, the transverse strength (three-pointbending) was measured according to Japanese Industrial Standard (JIS)R1601. The precipitated crystal phase in the sintered compact was alsoidentified by X-ray diffraction analysis. In the column of theprecipitated crystal phase in Table 2, “A” represents alumina, “W”represents wollastonite, and “F” represents forsterite.

After a predetermined number of green sheets for each sample werelaminated, firing was performed at the firing temperature shown in Table2. The resultant sintered compact was cut by a dicing saw and thedimensions were set at 10 mm long, 3 mm wide and 3 mm thick. Withrespect to the sintered compact of such size, the coefficient of thermalexpansion at 25° C. to 500° C. was measured.

Using the green sheets for each sample, a multilayered ceramic circuitcomponent 1 as shown in FIG. 1 was fabricated. That is, holes were madein the green sheets and an Ag-based paste was filled therein to formvia-hole joints 13 to 19, and then the Ag-based paste was screen-printedto form the external conductors 5 to 7 and the internal conductors 8 to12 in predetermined patterns. A predetermined number of the green sheetsfor forming ceramic layers 4 were laminated, followed by pressing.Firing was performed in air at the firing temperature shown in Table 2,and thus the multilayered ceramic circuit component 1 was obtained.

By applying a voltage with a frequency of 1 MHZ between the externalconductors 5 and 6 in the multilayered ceramic circuit component 1, theelectrostatic capacity and Q of the capacitor section 20 were measured,and the relative dielectric constant (∈_(r)) was calculated. Table 2shows the relative dielectric constant (∈_(r)) and Q.

In Tables 1 and 2, Sample Nos. 1 to 24 correspond to examples which arewithin the scope of the present invention, and Sample Nos. 25 to 33correspond to comparative examples which are out of the scope of thepresent invention.

As is clear from Table 2, in Sample Nos. 1 to 24 according to thepresent invention, the transverse strength was as high as 300 to 350MPa, ∈_(r) was in the range from 7.0 to 8.8, Q was as large as 1,400 to5,000, and the coefficient of thermal expansion was as large as 6.0 ormore. Thus, satisfactory characteristics for the ceramic substrate inthe ceramic circuit component were exhibited.

In Sample Nos. 22 to 24, in which an alkali metal oxide, such as Li₂O,K₂O or Na₂O, was incorporated in the glass, since the softeningtemperature of the glass was decreased (in comparison with Sample No. 4having the same glass composition apart from the fact that an alkalimetal was not incorporated), it was confirmed that firing could beperformed at the same temperature in spite of the decreased amount ofglass.

In Sample Nos. 12 to 21, in which TiO₂, ZrO₂, Cr₂O₃, CaF₂ or CuO wasincorporated in the glass, although not shown in Table 2, it wasconfirmed by X-ray diffraction analysis that the crystallization hadbeen accelerated.

In contrast, in comparative example Sample No. 25, since the amount ofalkaline earth metal, namely, M, in the glass was low, a dense sinteredcompact was not obtained when sintered at a temperature of 1,000° C. orless. In Sample No. 26, since the M amount in glass was high, the glassbecame unstable, and even if the firing temperature was optimized, thedensity of the sintered compact was not increased sufficiently, and thusthe transverse strength was as low as 250 MPa.

In Sample No. 27, a dense sintered compact was not obtained at a firingtemperature of 1,000° C. or less because of the excessively large amountof Al₂O₃ in the glass.

In Sample No. 28, a dense sintered compact was not obtained at a firingtemperature of 1,000° C. or less because of the excessively small amountof B₂O₃ in the glass. In Sample No. 29, Q was as low as 1,000 because ofthe excessively large amount of B₂O₃ in the glass.

In Sample No. 30, the relative dielectric constant (∈_(r)) was as largeas 9.1 because of the small amount of SiO₂ in the glass. In Sample No.31, having an excessively large amount of SiO₂ in the glass, thecoefficient of thermal expansion was as low as 5.8.

Because of the small amount of glass added in Sample No. 32, sinteringended in failure at a firing temperature of 1 ,000° C. or less. InSample No. 33, the transverse strength was as low as 280 Mpa because ofthe excessively large amount of glass added.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the forgoing and other changes in form anddetails may be made therein without departing from the spirit of theinvention.

What is claimed is:
 1. A composition for a ceramic substrate comprisinga mixture of: powdered borosilicate glass comprising about 5% to 17.5%by weight of B₂O₃, about 28% to 44% by weight of SiO₂, 0% to about 20%by weight of Al₂O₃ and about 36% to 50% by weight of MO, wherein MO isat least one member selected from the group consisting of CaO, MgO andBaO; and a powdered ceramic; in which the amount of the powderedborosilicate glass is about 40% to 49% by weight based on the totalamount of the composition for a ceramic substrate, and the amount of thepowdered ceramic is about 60% to 51% by weight based on the total amountof the composition for a ceramic substrate, and the composition aftersintering comprises a precipitated crystal phase comprising alumina andwollastonite.
 2. The composition for a ceramic substrate according toclaim 1, wherein the coefficient of thermal expansion after sintering isabout 6.0 ppm/° C. or more.
 3. The composition for a ceramic substrateaccording to claim 2, wherein the powdered ceramic comprises powderedalumina.
 4. The composition for a ceramic substrate according to claim3, wherein the borosilicate glass contains at least one alkali metaloxide selected from the group consisting of Li₂O, K₂O and Na₂O in apositive amount of about 5 parts by weight or less relative to 100 partsby weight of the total of the B₂O₃, SiO₂, Al₂O₃ and MO.
 5. Thecomposition for a ceramic substrate according to claim 4, wherein theborosilicate glass contains at least one compound selected from thegroup consisting of TiO₂, ZrO₂, Cr₂O₃, CaF₂ and CuO in a positive amountof about 5 parts by weight or less relative to 100 parts by weight ofthe total of the B₂O₃, SiO₂, Al₂O₃ and MO.
 6. The composition for aceramic substrate according to claim 5, wherein the borosilicate glasscomprises 6% to 16% by weight of B₂O₃, 35% to 43% by weight of SiO₂, 5%to 17% by weight of Al₂O₃ and 37% to 45% by weight of MO, MO comprisesCaO, the amount of the powdered borosilicate glass is 41% to 48% byweight, the amount of alkali metal oxide is 1 to 3 parts by weight andthe amount of said at least one compound selected from the groupconsisting of TiO₂, ZrO₂, Cr₂O₃, CaF₂ and CuO is 0.25 to 1 part byweight.
 7. The composition for a ceramic substrate according to claim 6,wherein the coefficient of thermal expansion after sintering is at least6.3 ppm/° C.
 8. The composition for a ceramic substrate according toclaim 1, wherein the borosilicate glass contains at least one compoundselected from the group consisting of TiO₂, ZrO₂, Cr₂O₃, CaF₂ and CuO ina positive amount of about 5 parts by weight or less relative to 100parts by weight of the total of the B₂O₃, SiO₂, Al₂O₃ and MO.
 9. Thecomposition for a ceramic substrate according to claim 2, wherein theborosilicate glass contains at least one alkali metal oxide selectedfrom the group consisting of Li₂O, K₂O and Na₂O in a positive amount ofabout 5 parts by weight or less relative to 100 parts by weight of thetotal of the B₂O₃, SiO₂, Al₂O₃ and MO.
 10. The composition for a ceramicsubstrate according to claim 2, wherein the borosilicate glass containsat least one compound selected from the group consisting of TiO₂, ZrO₂,Cr₂O₃, CaF₂ and CuO in a positive amount of about 5 parts by weight orless relative to 100 parts by weight of the total of the B₂O₃, SiO₂,Al₂O₃ and MO.
 11. The composition for a ceramic substrate according toclaim 1, wherein the borosilicate glass contains at least one alkalimetal oxide selected from the group consisting of Li₂O, K₂O and Na₂O ina positive amount of about 5 parts by weight or less relative to 100parts by weight of the total of the B₂O₃, SiO₂, Al₂O₃ and MO.
 12. Thecomposition for a ceramic substrate according to claim 1, wherein thepowdered ceramic comprises powdered alumina.
 13. The composition for aceramic substrate according to claim 1, wherein said Mo is Cao; andcontains SiO₂ and CaO in amounts such that wollastonite is precipitatedafter sintering.
 14. The composition for a ceramic substrate accordingto claim 1, wherein the borosilicate glass is lead-free.
 15. Thecomposition for a ceramic substrate according to claim 1, wherein theborosilicate glass is zinc free.
 16. The composition for a ceramicsubstrate according to claim 1 in the form of a ceramic green sheet. 17.A ceramic circuit component comprising: a substrate comprising a moldedand sintered composition for a ceramic substrate according to claim 1;and a conductive circuit inzassociation with the substrate.
 18. Theceramic circuit component according to claim 17 wherein the conductivecircuit comprises at least one metal selected from the group consistingof Ag, Au and Cu.
 19. A ceramic circuit component comprising: asubstrate comprising a molded and sintered composition for a ceramicsubstrate according to claim 2; and a conductive circuit in associationwith the substrate.
 20. The ceramic circuit component according to claim19, wherein the conductive circuit comprises at least one metal selectedfrom the group consisting of Ag, Au and Cu.